On the surface, the visit was to promote her book, "Lean In," for which Shim wrote a recommendation. Shim was designated as Sandberg's official Samsung counterpart for this trip to Korea.

But the sources said that, in reality, Sandberg was here to talk about hard business ? more specifically, on how Facebook may strike up a partnership with Samsung, one of the most powerful device makers in the world.

The meeting was therefore perceived as a speedy follow-up to previous talks Facebook chief executive Mark Zuckerberg held just over two weeks ago.

Zuckerberg had met with President Park Geun-hye as well as Shin Jong-kyun, Samsung's mobile unit chief.

Sources at the time had said the top Facebook official was seeking to co-develop a "Facebook-friendly" phone, among the ways the two firms could cement stronger ties.

"This time around, it's probably not about the phone anymore, but any other project with which Facebook can manage to catch Samsung's eye for a mobile partnership because Facebook is desperate," said one insider who declined to be identified.

Facebook has reportedly been facing a hoard of marketing problems, according to industry watchers, with advertising companies and firms pulling their ads after questioning the effect that Facebook has for their sales.

"We reached the conclusion that we don't want to place ads anymore because we felt the users weren't into them and therefore did not lead to sales. These users are in for the connection, not for the commerce," said one executive at a company with close relations with Facebook.

The fact that Sandberg's counterpart is Shim, Samsung's chief marketing officer, adds plausibility to the forecasts of their one-on-one nature.

Others said for Facebook, there really is no other device or operating system maker it could approach, other than Samsung.

"The choices are pretty much laid out for Facebook. It's either Google, Apple or Samsung, and Google is already quite chummy with Samsung, while Apple seems to be going downhill, so the last and most rational choice was Samsung," said another industry watcher on the condition of anonymity.

Sandberg is expected to meet with other Samsung officials who are further involved in the marketing and implementation of a new relationship between the two entities, with the roster including co-chief executive officer Shin Jong-kyun, who holds the keys to whether Samsung can do anything with Facebook.